Low temperature storage tank



1970 M. T. BUCKWALTER T L LQW TEMPERATURE STORAGE TANK 4 Sheets-Sheet l I 52 6% o i Filed Sept. 6, 1966 ATTORNEYS Jan. 27, 1970 cKw 'r ET AL 3,491,910

LOW TEMPERATURE STORAGE TANK 4 Sheets-Sheet 2 Filed Sept. 6, 1966 INVENTORS 47 1915 /V6/50/z MZiQ/Z Z'lzcfwa/iew ATTORNEYS Jan. 27, 1970 cKw ET AL 3,491,910

LOW TEMPERATURE STORAGE TANK 4 Sheets-Sheet 4 Filed Sept. 6, 1966 JWde/Z $15022 Wzfla/z Zfwwafw g/MM Wm ATTORNEYS- United States Patent 3,491,910 LOW TEMPERATURE STORAGE TANK Milton T. Buckwalter, Allison Park, and Ardell H. Nelson,

Coraopolis, Pa., assignors to Pittsburgh-Des Moines Steel Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 6, 1966, Ser. No. 577,366 Int. Cl. B65d 25/18 U.S. Cl. 220-9 10 Claims ABSTRACT OF THE DISCLOSURE The space between the inner and outer walls of a low temperature storage tank is provided with insulating means in the form of a plurality of units each of which comprises resilient thermal insulating material which is in precompressed condition until it is placed between the walls of the tank whereupon it is released. In operative position, the insulating means is continuously under compression between the inner and outer walls, The unit is initially retained in compressed condition by a tubular wrapper which is severed and in final position engages the opposite walls of the tank. The units may include a plurality of layers of dilferent material, and the tubular retaining means may be of various forms.

The present invention relates to new and novel low temperature storage tank apparatus, and more particularly to a low temperature storage tank including novel thermal insulating means.

The invention is directed to a tank for storing liquids at low temperature. Low temperature storage may be defined as storage of liquids at a temperature of +32 F. or lower. The tank of the present invention includes a unique insulating means which effectively operates when subjected to great variations in temperature which normally occur during operation of this type of tank.

It is often desirable and advantageous to store normally gaseous elements, hydrocarbons and similar materials in a liquefied state at temperatures at or near the boiling point of the liquid. These substances may be stored at substantially atmospheric pressure. By storing such gases in the liquid phase, the volume is greatly reduced thereby resulting in considerable economy since the size of the storage tank can also be considerably reduced. For example, nitrogen stored at its liquid boiling point of 32() F. has a gas-to-liquid volume ratio of approximately 695: 1. Methane stored at its liquid boiling point of 258 F. has a gas-to-liquid ratio of approximately 638:1. Oxygen stored at its liquid boiling point of 297 F. has a gas-toliquid volume ratio of approximately 863: 1, and hydrogen stored at its liquid boiling point of 423 F. has a gas-toliquid volume ratio of approximately 848:1.

In order to take advantage of the large volume reduction indicated by the previous figures, it is necessary to store the extremely cold liquid in a heavily insulated tank. One type of tank used for this lower temperature storage is a double wall tank, having an inner wall designed to contain the liquefied gas to be stored and also designed to withstand the lateral and vertical pressures of the insulation material acting against the outer surface of the inner wall, and having an outer wall serving as an insula tion protection barrier and which is designed to withstand the lateral and vertical pressures of the insulation material acting against the inner surface of this wall.

The space formed between the inner wall and the outer wall is filled with various types of insulation material. Most of the insulation system presently in use present problems varying in degrees of severity. Some examples of insulation materials presently in use are lightweight inorice ganic thermal insulators having a small particle size such as expanded perlite or expanded vermiculite. Some other insulations which are used include granulated cork, foamed polystyrene beads, and shredded materials such as fiber glass waste and mineral wool.

With a double wall tank such as described herein, the use of the insulation materials listed above presents problems due mostly to the extensive thermally induced lateral movements of the inner wall of the tank as a result of the extreme temperature variations occurring during use of the tank. The extremely low temperatures to which the inner wall is subjected cause a thermal contraction when the cold liquid is placed inside the tank and a thermal expansion when the liquid is withdrawn from the tank and the tank is permitted to warm up to ambient temperature. Furthermore, when the liquid level is low, a temperature gradient exists between the lower portion of the inner wall in contact with the liquid and the upper portions of the inner wall which are some distance removed from the cold liquid. In this case, the differential thermal expansion takes place at various levels in the inner wall.

Expansion and contraction of the inner wall of the tank also occur as the liquid is put into the tank and withdrawn therefrom. As the liquid is put into the tank, the inner wall will expand under load from the liquid contents, and correspondingly the inner wall again will contract as the liquid is withdrawn from the tank and the load on the inner wall is decreased.

In considering the problems involved in this type of storage tank, the size of the tank is a major factor. The storage tank to which the present invention is particularly directed may have an inner diameter on the order of 30 ft. to 300 it, while the height of such tank may be on the order of 30 ft. to ft., while the inner and outer side walls of the tank may be spaced apart on the order of 2 to 5 ft. It is accordingly apparent that the size of the components is very large and that the loading thereon can be very great when the tank is full of liquid. It is also evident that the large changes in temperature cause considerable movement of the walls of the tank of such dimensions.

Because of the variations in the dimensions of the annular space between the inner wall and the outer wall of the tank which occur due to the thermally induced movements of the inner wall, various insulation material particles placed within this annular space have a tendency to settle vertical downward when the inner wall thermally contracts. When thermal expansion takes place, there is not a compensating vertical upward movement of the insulation material, but instead a compaction and crushing effect results from the increased lateral pressure developed in the insulation by the outward movement of the inner wall. As this cycle (insulation movingdownward during the cooling of the inner wall and being compacted as the inner wall warms up) repeats itself, the amount of compaction and crushing of the insulation becomes significant and portions of the annular space near the top of the tank become completely devoid of insulation material. As the thermal expansion and contraction continues, the insulation material produces an ever increasing lateral pressure against the outer surface of the inner wall which could cause buckling or rupturing of the inner wall. The exact amount of thermal expansion and contraction which may take place in the inner wall depends on such factors as the range of temperatures in the cycle, the size of the inner wall, and the coefficient of thermal expansion of the material of which the inner wall is constructed.

U.S. Patent No. 3,147,878 details an insulation system which consists of a granular insulation used in conjunction with a resilient blanket material. This insulation system has several drawbacks in its use which are described hereinafter.

The blanket of the aforementioned US. patent is generally attached to the outer surface of the inner wall by many fasteners such as welded studs which project laterally from the inner wall and which penetrate the blanket. These fasteners are necessary during the installation of the blanket and they are also required to hold the blanket in place while the granular insulation material is added to fill the balance of the annular space. The great number of fasteners which must be attached to the outer surface of the inner wall are expensive to install and must be adequately inspected to ensure that no detrimental effects have occurred to the inner wall material.

Another drawback to this prior art system is that the granular type of insulation material which is used in conjunction with the blanket settles and consolidates for about or 6 thermal cycles. This means that replenishment of the insulation material in the upper portion of the insulation space is necessary to preclude leaving void spaces in the insulation system. In order to be fully effective, this resilient blanket must he placed against the outer surface of the inner vessel. As the blanket is placed further away from the outer surface of the inner vessel, it becomes increasingly ineffective. This means that the blanket itself, being placed against the inner vessel, must operate at or near the temperature of the tored product.

In the present invention, a novel arrangement is employed wherein the insulating means disposed between the inner and outer walls of the tank comprises resilient material which frictionally engages both the inner and outer walls, the insulating means being precompressed so that when it is in operative position, it has residual compression which causes the insulating means to be continuously urged into frictional contact with the inner and outer walls of the tank regardless of the relative movements of these inner and outer Walls with respect to one another. In other words, sufiicient residual compression is provided in the material of the insulating means so that regardless of the amount of movement which normally occurs between the inner and outer walls, the insulating means will at all times remain under compression and in frictional contact with these walls.

With this arrangement, the insulating means is selfsupporting within the annular space between the inner and outer walls of the tank and will not shift during thermal cycling of these walls. This eliminates the formation of voids in the insulating material and there is no necessity for replenishing the insulating material after it has been initially installed.

Furthermore, since there is no downward shifting of insulating material within the space between the inner and outer walls, increased lateral pressure against the outer surface of the inner wall does not occur during operation of the tank thereby eliminating the hazard of buckling or rupture of the inner wall as discussed hereinbefore. Accordingly, the inner wall construction may be less rigid than required in the prior art resulting in a considerable saving in cost.

No fasteners or attachments on either the inner or outer walls of the tank are required in the present invention thereby reducing the initial cost and further preventing any damage to the material of the inner wall as may occur when fasteners are secured thereto.

The insulation means of the present invention may also be readily installed since the insulating means is self-supporting, and a workman may be supported on the insulating material by placing a relatively rigid support means thereover to distribute the weight evenly over the insulating means.

The aforementioned precompression and continuous compression of the insulating means provides a safety factor to ensure that the insulating means at all times remains in good frictional engagement with the inner and outer walls of the tank regardless of the lateral movements of the walls with respect to one another.

The present invention also contemplates a novel method of installing the insulation means whereby the insulation can be quickly and easily installed by relatively unskilled personnel and in a substantially fool-proof manner.

An object of the present invention is to provide new and novel low temperature storage tank apparatus which effectively operates when subjected to great variations in temperature.

Another object of the invention is the provision of a low temperature storage tank incorporating novel insulating mean-s which prevents shifting of the insulation material and creation of voids particularly near the top of the tank.

Still another object of the invention is to provide a low temperature storage tank wherein a more lightweight less rigid construction may be employed in the walls of the tank without the danger of buckling or rupture thereof.

Yet another object of the invention is the provision of a low temperature storage tank wherein no fasteners or attachments are required on the walls for supporting the insulation means in place.

A still further object of the invention is to provide a low temperature storage tank wherein the insulation means may be readily installed and the installed insulation means includes a built-in safety factor which ensures good frictional engagement with the walls of the tank at all times.

Another object of the invention is to provide a new and novel method of installing insulation in a low temperature storage tank.

Other objects and many attendant advantages of the invention will become more apparent when considered in connection with the specification and accompanying drawings, wherein:

FIG. 1 is a vertical section through a storage tank according to the present invention;

FIG. 2 is a sectional view taken substantially along line 2-2 of FIG. 1 looking in the direction of the arrows;

FIG. 3 is a top perspective view of an insulation unit according to the present invention;

FIG. 4 is an elevation illustrating the manner in which the individual insulation units are mounted in place by a Workman;

FIGS. 5 through 8 inclusive illustrate in a somewhat schematic manner the precompression of an individual insulation unit and the residual compression therein when mounted in place regardless of the lateral movements of the inner and outer walls of the tank;

FIG. 9 is a top perspective view of a modified insulation unit according to the present invention;

FIG. 10 is a top perspective view of another form of insulation unit according to the present invention;

FIG. 10a is a section through a unit such as shown in FIG. 10 when mounted in operative position between the inner and outer walls of a tank;

FIG. 11 is a top perspective view of a further form of insulation unit according to the present invention;

FIG. 12 is a view of the insulation unit shown in FIG. 11 with the wrapper material thereabout;

FIG. 13 is a top perspective view partly broken away of still another form of insulation unit according to the present invention; and

FIGS. 14-18 inclusive are top perspective views of various arrangements of insulation units and other insulating substances which may be employed between the walls of the tank of the present invention.

Referring now to the drawings wherein like reference characters designate corresponding parts throughout the several views, a low temperature storage tank according to the present invention is illustrated generally by reference numeral 20 in FIG. 1 of the drawings. The tank includes an inner substantially cylindrical Wall 22 having three spaced peripherally extending stitfeners 24, 26 and 28 secured to the inner surface thereto to rigidify the structure. The inner wall 22 rests upon and is suitably secured as by welding or the like to a base plate 30. A substantially dome-shaped means 32 is suitably secured as by welding to the upper edge of side wall 22. The portions 22, 30 and 32 may be of aluminum or a 9% nickel steel alloy or the like which has suitable characteristics when in contact with liquids at extremely low temperatures.

The tank also includes an outer side wall 40 which is of generally cylindrical configuration and which is spaced from and is concentric with the inner side wall 22. The lower edge of side wall 40 is suitably secured as by welding to a base plate means 42 spaced from the base plate means 30 previously described. A substantially domeshaped upper wall 46 is suitably secured as by welding to the upper edge of the outer side wall 40 and is spaced above the upper wall portion 32 previously described. The outer wall portion of the tank may be formed of carbon steel or similar substance having the necessary strength and rigidity to accommodate the loads encountered in use.

It should be noted that the inner and outer wall portions hereinafter referred to may designate either the side walls or the top walls since the insulation means of the present invention may be employed both in the spaces between the side walls and the top walls if so desired. The space between the base plate means 30 and 42 is filled with a suitable load bearing insulation such as perlite concrete, foam glass blocks and the like. This body of load bearing insulation is indicated by reference numeral 48 in FIG. 1.

A suitable access means in the form of a manhole or the like is provided in the upper wall 46 of the tank, and a manhole cover such as indicated by reference numeral 50 may be suitably secured in this access opening whereby a workman may gain access to the space between the walls of the tank. In this connection, it should be understood that the tank may be on the order of 30 ft to 300 ft. in diameter within the inner wall portion of the tank, and the space between the inner and outer wall portions of the tank may be approximately 2 to 5 ft., whereby a workman can readily move about within such space.

The space between the upper wall portions 32 and 46 may be filled with a suitable thermal insulating material such as expanded perlite, and also suitable shredded materials may be employed within this space. The body of insulating material disposed in this space is indicated by reference numeral 52 in FIG. 1.

A conduit means 60 extends through the outer and inner walls at the lower left-hand portion of FIG. 1 and opens within the tank, a valve or suitable control means 62 being connected in this conduit for controlling the flow of liquid therethrough. This conduit means may be employed both to fill the tank and to withdraw liquid therefrom.

A conduit means 64 extends through the upper wall portions 46 and 32 and opens into the upper part of the tank, this conduit means having a suitable control means such as valve 66 connected therein. Conduit means may be employed for drawing off vapor from the upper portion of the tank at suitable intervals. The upper level of the liquid in the tank is indicated by reference numeral 68.

As illustrated in FIG. 1, the novel insulating means of the present invention is incorporated between the side wall portions 22 and 40. The insulation means includes a plurality of insulating units 70 which are illustrated in their operative positions in FIG. 1. As seen particularly in FIG. 5 which illustrates schematically an end view of an individual insulating unit, a typical construction of an insulating unit may include a plurality of individual layers of material 72 which are disposed in abutting relationship with one another. This material is chosen for its thermal insulating qualities and also for its resilient characteristics. It is contemplated that the material used will be a good thermal insulator and will also be quite resilient. In a typical example, each of the layers 72 may comprise a sheet of matted glass fibers arranged in random fashion and held in operative relationship by means of a phenolic resin binder. Fine glass fibers of small diameter should be used, and satisfactory operating characteristics are obtained with fiber glass mats having a density between approximately 1 and 2 lbs. per cubic foot. The insulating material could also be made of synthetic acetate fibers with a proper binder.

After the layers of material are assembled in abutting relationship as seen in FIG. 5, they are suitably compressed laterally so as to reduce the volume of the layers of material to approximately /3 their initial volume. The stacked layers of material are then inserted within a suitable tubular wrapper means 74 for retaining the insulating material in such compressed condition. This precompression of the insulating material of the individual insulating units of course facilitates shipping thereof since the volume is substantially reduced. As shown in FIGS. 3 and 6, the wrapper material 74 causes the insulating unit to form a generally oval-shaped cross sectional configuration whereas the original cross sectional configuration of the stacked layers of material as shown in FIG. 5 was originally rectangular. As illustrated, the wrapper material may comprise paper, although other suitable substances may be employed for the wrapper material.

Referring now to FIG. 4, the manner in which the individual insulating units are placed in operative position is illustrated. As shown in this figure, a number of units have already been placed in operative position, and a workman has placed a relatively rigid supporting surface such as a wooden plank on the top surface of one of the insulating units. An insulating unit 70 is being placed in operative position by the workman. The unit 70' has been placed in the inclined position illustrated and a suitable cutting tool 82 is being run up along the undersurface of the units so as to slit the wrapper longitudinally of the unit. After cutting the wrapper longitudinally along the bottom of the unit, the workman proceed to make a similar out along the top of the unit. This of course severs the wrapper into two halves, and allows the precompressed resilient material of the unit to expand sideways into engagement with the inner and outer walls of the tank. It will of course be understood that as seen in FIG. 4, the outer wall 40 has been removed and a workman is illustrated as being located in the space between the inner and outer walls of the tank.

It should also be understood that the wrapper may incorporate a built-in means in certain portions thereof such as a Zipper means or string which could be manually pulled to separate the wrapper into two halves thereby eliminating the necessity of providing a separate cutting tool.

The precompression of the material will cause the sides of the unit having the wrapper material thereon to be urged into tight frictional contact with the surfaces of the inner and outer walls of the tank. This frictional pressure is suflicient to cause each individual unit to be selfsupporting, and in fact the friction is sufficiently great so that any one individual unit will support several other units thereabove if necessary. However, the frictional engagement is not so strong to prevent an individual unit' from moving downwardly with the weight of a Workman thereon. Accordingly, after the workman has cut the wrapper along the top and bottom of the unit, he can then place his weight on the upper surface of the unit and force it down into its final operative position. It is apparent that the workmen can continue to set the insulating units in operative position throughout the periphery of the tank and can continually move the plank 80 from one place to another as required in carrying out this procedure.

The individual insulating units are placed adjacent one another in abuttting relationship as shown in FIG. 4 so as not to present any substantial voids between the individual insulating units.

As mentioned previously, the insulating material is initially precompacted in a lateral direction as seen in FIG. 5 to reduce the dimension thereof to approximately the initial dimension, the reduction in lateral dimension being indicated by the arrow a in FIG. 5. The amount of precompression and the initial size of the material being precompressed are so adjusted that when the insulating units are in operative position as shown in FIG. 7, a certain amount of residual compression indicated by arrow b remains in the material. In other words, the insulating unit 70 will tend to expand back to its original lateral dimension as shown in FIG. 5, and the distance 17 illustrated in FIG. 7 represents the difference between the amount of expansion which has taken place and that which the insulating material would tend to expand if free to do so. As seen in FIG. 7 the insulating unit is contained between the outer and inner wall portions 40 and 22 of the tank and since it is still under compression will exert a continuous outward pressure so as to resiliently urge the side surfaces of the insulating unit into tight frictional engagement with the inner and outer walls of the tank. FIG. 7 illustrates the inner and outer walls in their nearest proximity to one another, and in FIG. 8, the inner wall 22 has contracted away from the outer wall 40 a distance d, and this represents the maximum spacing of the inner and outer walls during normal use of the apparatus. It will be noted that when the inner and outer walls are at this maximum displacement from one another, a residual compression still exists in the insulating material of the unit, this residual compression being represented by the distance which represents the amount of expansion which the insulating unit would incur if not restrained. It is accordingly apparent that the residual compression in the inculating material of the individual units will at all times cause the units to be tightly held in the proper operative relationship so that no shifting of the insulating material can occur. Furthermore, the insulating units when in operative position will be selfsupporting and when a plank is disposed thereover will further support the weight of a workman so as not to shift while the insulating units are being installed. This residual compression also provides a built-in safety factor to ensure contact with the walls of the tank at all times regardless of the relative lateral movements of the tank walls. The residual compression also exerts a pressure on the inner wall of the tank which is substantially less than the lateral pressure on the inner walls of tanks employing prior art arrangements. This of course enables the inner wall of the tank to be of less rigid construction thereby reducing the initial cost. The downward load which has to be carried by the inner and outer shells may be reduced by a factor of as much as 6 when compared with the same thickness of conventional insulation systems.

As illustrated, a double flat bottom type of tank has been employed, although this base construction may be modified if desired. The insulating means of the present invention may also further be employed with storage tanks of other Shapes and incorporating the same advantages.

It is evident that the insulating means of the present invention may be mounted in operative position without employing any fasteners or attachments on either the inner or outer walls of the tank thereby completely eliminating the problems of potential damage to these walls when mounting such auxiliary attachment means in place.

In a typical example wherein the tanks of the wall are spaced approximately 2 ft. apart, the initial lateral thickness of a unit as seen in FIG. may be approximately 30 inches so that when it is installed between walls of a tank which are about 2 ft. apart, a residual compression is present in the resilient material of the insulating unit which would tend to return to its initial 30-inch thickness. An insulating unit having a 30-inch thickness may typically be 2 ft. in height and approximately 6 ft. in length so that the unit as described would weigh about 30 lbs. thereby enabling easy manipulation thereof by the average workman.

It is contemplated that the residual compression remaining in the insulating units would be on the order of 10% to 30% so as to ensure that the opposite sides of the units will be firmly frictionally engaged with the walls of the tank at all times. The resilient nature of the thermal insulating material as well as the wrapper means thereabout enables the insulating means to readily conform about any irregularities or projections extending from the walls of the tank. This of course also enables the insulation means to readily conform to conduit means and the like and which may extend through the walls of the tank.

As illustrated, the layers of material of the various insulating units extend substantially parallel with the adjacent wall portions of the tank. These layers may also extend substantially radially of the tank, although it is considered that this arrangement would not be as effective. While the frictional engagement between the wrapper means and the tank walls is considered adequate as illustrated, it should be understood that the frictional contact could be enhanced by providing a frictional surface on the outer face of the wrapper material if so desired.

Referring now to FIG. 9 of the drawings, a modified form of insulating unit is illustrated by reference numeral 90. In this form of the invention, a pair of layers of material 92 and 94 are provided which may be of substantially the same construction as the layers 72 previously described. A third layer 96 of thermal insulating material is sandwiched between the layers 92 and 94. Layer 96 may be formed of a different thermal insulating material such as polyurethane or the like which has the desired thermal insulating characteristics and is sufficiently flexible to provide the desired end results. These layers of material 92, 94 and 96 are then placed within a wrapper means as in the previously described modification and precompressed for the aforementioned purposes.

Referring now to FIGS. 10 and 10a, a further modified form of insulating unit according to the present invention is illustrated. This insulating unit indicated generally by reference numeral 100 includes a plurality of layers of material 102 which may be of similar construction to the layers 72 previously described. The layers of resilient thermal insulating material are precompressed in the same manner as previously described and then held in such precompressed condition by a wrapper means 104 disposed tightly thereabout. In this modification, the wrapper means may comprise open mesh cloth. As seen in FIG. 10a, the cloth wrapper material has been slit along the upper and lower medial longitudinal portions thereof so that the resilient material of the layers 102 causes the opposite sides of the insulating units to be engaged with the outer and inner walls 40' and 22' corresponding to the walls 40 and 22 previously described. The open mesh cloth material 104 will provide a very good frictional contact with the surfaces of the walls for retaining the insulating unit in operative position.

Referring now to FIGS. 11 and 12, a further modified form of insulating unit is illustrated. As seen in FIG. 11, the thermal insulating material in this instance comprises a single block of suitable thermal insulating material of the desired resilient characteristics at the temperatures involved. The material of block 110 may be foamed polyurethane or a similar plastic substance. As seen in FIG. 12, the block 110 is then precompressed within a wrapper means 112 which may be of either paper or cloth or similar material as desired. Here again, the resilient insulating material is initially precompressed and then later expanded between the walls of the storage tank to provide the desired results.

Referring now to FIG. 13, a still further modified form of the invention is illustrated wherein the insulating unit is indicated generally by reference numeral 120. This insulating unit comprises a plurality of layers of material of different substances, the over-all unit aifording the same beneficial results as those previously described.

A layer of foam plastic material similar to that previously described is illustrated by reference numeral 124 and is disposed adjacent a layer 124 of a material similar to that of the layers 72 previously described, layers 122 and 124 being separated by a layer 126 of heat reflecting material such as aluminum foil. A layer- 128 similar to layer 124 is separated therefrom by another layer 130 of aluminum foil or the like. A further layer 132 similar to layer 128 is separated therefrom by a layer 134 of aluminum foil or the like. Still another layer 136 similar to layer 132 is separated therefrom by a layer 138 of heat reflecting material. A layer 140' which may again comprise foam plastic material is separated from layer 136 by still another layer 142 of aluminum foil or the like.

The opposite sides of the insulating unit 120 may be provided with layers 144 and 146 of heat reflecting material such as aluminum or the like, and as illustrated, the layer 146 is sprayed on the outer surface of layer 140 by means of a spray gun 148. The over-all insulating unit 120 is then precompressed within a suitable wrapper means and employed in the same manner as previously described.

FIGURES 14-18 inclusive illustrate different manners in which the insulating units according to the present invention may be arranged, it being understood that the various insulating units as shown in these figures may be of any construction as hereinbefore described.

Referring to FIG. 14, the insulating units 150 are each disposed such that their longitudinal axes are vertical rather than horizontally disposed as in the modification illustrated in FIG. 1. It will of course be understood that only the insulating units are shown, the inner and outer wall structure of the tank having been eliminated for the purpose of illustration.

Referring now to FIG. 15, a further modification is illustrated wherein a plurality of insulating units 154 are arranged in generally horizontal disposition, these individual insulating units defining substantially horizontal annular rings of insulating material. The rings of insulating material defined by insulating units 154 alternate with horizontal layers of insulating material 156 which may be of expanded perlite and the like, or other suitable loose insulating materials. The rings of insulating material of the individual units 154 will serve to adequately support the horizontal layers of loose material 156.

Referring now to FIG. 16 of the drawings, still a further modified form of the invention is illustrated wherein individual insulating units 160 according to the present invention are arranged in vertical stacks with adjacent vertical stacks being spaced from one another for receiving vertical layers 162 of other suitable insulating material such as expanded perlite and the like. It will be noted that the major portion of the insulating material adapted to be disposed between the inner and outer walls of the tank comprises the insulting units of the present invention, and it is not considered that the relatively narrow vertical layers of loose material 162 will cause the problems encountered wherein the entire space between the walls of the tank is filled with such material.

Referring now to FIG. 17, a still further modified form of the invention is illustrated wherein the individual insulating units 170 are of the construction hereinbefore described. These individual insulating units are arranged so as to provide alternate generally horizontally extending layers 172 of other insulating materials such as expanded perlite and alternating vertically extending layers of 10 similar loose insulating material is indicated by reference numerals 174.

Referring now to FIG. 18, still another modified form of the invention is illustrated wherein the individual insulating units according to the present invention are spaced from one another and various generally horizontally extending layers 182 of other insulating materials such as expanded perlite are provided, and spaced generally vertically extending layers 184 of similar insulating material are provided.

Various arrangements have been illustrated in FIGS. 14-18 wherein the individual insulating units could be disposed in different relationships with respect to one another and further in combination with other types of insulating material. The different layers of insulating material can be of any suitable construction, either in block form or as loose material. It will be understood that various other relationships between the insulating units of the present invention and various other kinds of insulating material may be employed, but in all instances insulating units are employed according to the present invention for retaining the insulating material in the desired operative position.

It is apparent from the foregoing that there is provided according to the present invention new and novel low temperature storage tank apparatus which effectively operates when subjected to great variations in temperature. The novel insulating units of the present invention prevent shifting of the insulating means during operation of the tanks and thereby eliminate creation of voids particularly near the top of the tank. This of course eliminates the necessity of replenishing insulating material in the tank and prevents the downward movement of insulation which in the prior art has contributed to the buckling or rupture of the walls of the tank. Accordingly, the construction of the walls of the tank may be less rigid than heretobefore required in the art substantially reducing the cost of the tank. No fasteners or attachments are necessary on either the inner or outer walls of the tank for supporting the insulating means in operative position thereby eliminating this expense and preventing any damage to the walls of the tank as is often the case when these fasteners or attachments are mounted in place. The insulating means may be readily installed due to the fact that it is self-supporting and will support the weight of a workman without settling while being installed. The residual compression present in the insulating material provides a safety factor which ensures that the opposite sides of the insulating means will be urged into tight frictional contact with the inner and outer walls at all times regardless of the lateral movement of the walls of the tank. A novel method of installing insulation means in low temperature storage tanks is also provided, this method being capable of being carried out in a simple and effective manner by relatively unskilled personnel.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, and since the scope of the invention is defined by the appended claims, all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.

What is claimed is:

1. Low temperature storage tank apparatus comprising a tank having inner and outer wall portions spaced from one another to define a space therebetween, insulating means disposed within the space between said inner and outer wall portions, said insulating means being frictionally engaged with said inner and outer walls, the insulating means comprising resilient thermal insulating material, the insulating means being precompressed so that when in operative position it is continuously under compression in a direction perpendicular to said inner and outer walls and the insulating means is continuously urged into frictional contact with said inner and outer walls during use of the tank as the inner and outer walls move relative to one another in accordance with the operating conditions of the tank, said insulating means comprising a plurality of individual units disposed adjacent one another, opposite sides of each one of said units being in frictional contact with said inner and outer walls, each unit including wrap material on the sides thereof, said wrap material being in engagement with said inner and outer walls, the ends of adjacent units being free of wrap material and having the insulating means thereof directly exposed and adjacent to one another.

2. Apparatus as defined in claim 1 wherein said heat insulating means comprises a plurality of units disposed adjacent one another, each of said units comprising a onepiece construction of said resilient thermal insulating material having wrap material on surfaces thereof.

3. Apparatus as defined in claim 1 wherein said insulating means comprises a plurality of units, each of said units having wrap material thereon along certain surfaces thereof, said wrap material comprising paper.

4. Apparatus as defined in claim 1 wherein said insulating means comprises a plurality of units, each of said units having wrap material thereon along certain surfaces thereof, said wrap material comprising cloth.

5. Apparatus as defined in claim 1 wherein said insulating means comprises a plurality of units disposed adjacent one another, each of said units including a plurality of layers of material, each unit having wrap material on op 12 posite surfaces thereof in engagement with said inner and outer wall portions.

6. Apparatus as defined in claim 5 wherein at least one of said layers of material in a unit is of a different substance than another layer of material in said unit.

7. Apparatus as defined in claim 6 wherein at least one of said layers of material comprises a layer of heat reflecting material. K 1

8. Apparatus as defined in claim 1 wherein said insulating means comprises a plurality of units disposed adjacent one another with certain ones of said units being spaced from one another and including a different substance which is a thermal insulating material disposed in the space between said units.

9. Apparatus as defined in claim 8 wherein said spaces between said units extend horizontally of the tank.

10. Apparatus as defined in claim 8 wherein said spaces between said units extend vertically of the tank.

References Cited UNITED STATES PATENTS 2,132,958 10/1938 Martin "20646 2,354,186 7/1944 Donahue 20646 JOSEPH R. LECLAIR, Primary Examiner JAMES R. GARRETT, Assistant Examiner U.S. Cl. X.R. 

